1 Police officers help keep us safe. It is their job. There are many different things that they do to keep people safe. They capture criminals. They patrol neighborhoods and parks to deter crime. They direct traffic around schools, events, and accidents. These are the kind of things that make people glad there are police officers around.2 Sometimes, though, people don't like the things that police officers do to keep us safe. This is especially true when it comes to the speed at which we drive our cars. Speed limits on streets and highways are posted in order to keep people safe. That is why speed limits are lower around schools, in the downtown areas of a city, and on very curvy roads. Speed limits help protect drivers and pedestrians. To keep people safe, police officers must make sure that people follow the posted speed limits on streets and highways. They do this by issuing tickets to people who drive over the speed limit. When a person is given a ticket for speeding, they must pay a fine. Police officers hope that paying the fine will make the driver slow down and obey the speed limit.3 So how does a police officer know that a driver is moving too fast? Can they tell by just looking at a moving car? Do they guess? In most cases, police officers use a special tool to help them find divers who are moving too fast. The tool is called a radar gun. Police officers have radar guns inside their patrol cars. They point the gun at passing cars and the gun displays the speed of each car as it passes. How does that work?